Time dependent deflection control for ink jet printer

ABSTRACT

An ink jet printer in which ink droplets issuing from a source serially pass through an electrically energizable deflection field which is activated at regularly recurring intervals. Deflection of the drops occurs along different trajectories toward a recording medium because of the variable time each droplet is subjected to the energized deflection field. The droplets which are deflected have the same physical or electrical characteristics and are not given differing charges, for example, before entry into the deflection field. Both electrically chargeable droplets and magnetic droplets may be used as the marking fluid when directed according to time dependent deflection. Generally, the deflection field is of sufficient length to include simultaneously all droplets which will comprise a full character stroke on the recording medium and the deflection signal is a square wave selectively applied. However, deflection fields may be shortened and the applied signal may either increase or decrease with time during the energizing interval. In addition, apparatus may be included to produce deflection along either of two coordinate axes and means are disclosed to select droplets required for printing while discarding others during issuance of the droplets from the source at a fixed generation rate.

United States Patent 1 McDonnell et al.

[ 1 Feb. 4, 1975 TIME DEPENDENT DEFLECTION CONTROL FOR INK JET PRINTER[75] Inventors: James A. McDonnell, Binghamton;

Robert E. McGuire; Raymond Radlinsky, both of Endwell, all of NY.

[73] Assignee: International Business Machine Corporation, Armonk, NY.

[22] Filed: Sept. 26, 1973 [21] Appl. No.2 401,006

Primary Examiner-Joseph W. Hartary Attorney, Agent, or Firm-K. P.Johnson INK SOURCE [57] ABSTRACT An ink jet printer in which inkdroplets issuing from a source serially pass through an electricallyenergizable deflection field which is activated at regularly recurringintervals. Deflection of the drops occurs along different trajectoriestoward a recording medium because of the variable time each droplet issubjected to the energized deflection field. The droplets which aredeflected have the same physical or electrical characteristics and arenot given differing charges, for example, before entry into thedeflection field. Both electrically chargeable droplets and magneticdroplets may be used as the marking fluid when directed according totime dependent deflection. Generally, the deflection field is ofsufficient length to include simultaneously all droplets which willcomprise a full character stroke on the recording medium and thedeflection signal is a square wave selectively applied. However,deflection fields may be shortened and the applied signal may eitherincrease or decrease with time during the energizing interval. Inaddition, apparatus may be included to produce deflection along eitherof two coordinate axes and means are disclosed to select dropletsrequired for printing while discarding others during issuance of thedroplets from the source at a fixed generation rate.

15 Claims, 10 Drawing Figures NOZZLE OUTGOING TRAJECTORIES TIME SEQUENCEDEFLECTION SIGNAL GEN.

PATENTEDFEB 4% 3.8641592 SHEET 10F a INK SOURCE 2 Z OUTGOING L/ Z/TRAJECTOR'ES o o o T r 14 TIME SEQUENCE/I6 DEFLECTION FIG. i SIGNAL GEN.

DEFLECTION VOLTAGE T|MEP PRINT 2 POSITION o 0 0 o o O 0 DROP NUMBER o oo o o 0 0 o o HORIZONTAL VERTICAL DEFLECTION DEFLECTION SIGNAL GEN.SIGNAL GEN.

PATENTEDFEB 4W5 3.864.692

E o o CONTROLLED CHARGE VOLTAGE F I G 5 DROPLET SELECTI 44 VOLTAGECONTROLLED CHARGE VOLTAGE PATENTED 4|975 3.864.692

sum 30F 3 INK SOURCE;

NOZZLE v TIME'SEOUENCE DEFLECTION 65"SIGNAL GENERATOR FIG. 7

TIME SEQUENCE DEFLECT|0N 65 SIGNAL GENERATOR FIG. 8

TIME DEPENDENT DEFLECTION CONTROL FOR INK JET PRINTER BACKGROUND OF THEINVENTION The present invention relates to graphic display recorders andmore particularly to ink jet printers employing selectively directeddroplets for forming characters and the like on a recording medium.

Ink jet printers are well known. Examples of such printers are disclosedin U.S. Pat. No. 2,600,129, issued June 10, 1952 to C. H. Richards; U.S.Pat. No. 3,596,275, issued July 27, 1971 to R. G. Sweet; U.S. Pat. No.3,500,436, issued Mar. 10, 1970 to R. W. Nordin; and U.S. Pat. No.3,510,878, issued May 5, 1970 to C. E. Johnson, Jr.

Character printing with a stream of ink droplets is generallyaccomplished electrostatically in the prior art by selectivelydeflecting the stream repeatedly along one direction while the recordingmedium on which the ink is deposited moves at a slower velocity along asecond orthogonal direction. This results in a matrix type of printingin which droplets not required are directed to a gutter or else notproduced. Each desired droplet is given an electrical charge at the timeof formation that corresponds with its assigned position along the lineof deflection and directed through an electrostatic field of constantstrength. The several droplets are there deflected in proportion totheir respective charges.

This type of printing requires sophisticated electrical circuitry. Thecharges for each desired droplet must be accurately established andmaintained through the duration of printing in order to provideuniformly spaced and accurately placed droplets on the record medium.Because of the aerodynamic effects and interdrop electricalcharacteristics, compensation circuits are usually required to maintainthe uniform spacing of droplets. In addition, changes in ink temperatureor viscosity affeet the time of drop breakoff and hence the chargeplaced on the droplet; this is overcome by using synchronizing circuitswhich rely on further detection devices to maintain proper dropletcharge.

When printing with magnetic ink droplets, it has been found thatalthough no charging is required, the magnetic deflection field must bevaried for each droplet in order to attain the proper droplet spacing.This, therefore, requires a series of magnetic deflection elementsbetween the droplet formation point and recording medium for theselective application of various and suitable deflection energies. Thisis done by either providing a single magnetic field and varying the fluxdensity or by providing a succession of magnetic fields which can beselectively energized as each droplet progresses toward the recordsurface. As with the electrostatic printing, such control circuitsbecome complex, expensive and are usually difficult to maintain at theproper stability.

It is accordingly a primary object of this invention to provide improvedink droplet printing apparatus for producing graphic displays such asalphanumeric characters.

Another important object of this invention is to provide ink dropletprinting apparatus in which droplet deflection is accomplished byenergizing the deflection field at selected predetermined times and thedroplets, having uniform charges or latent magnetization, are

given trajectories toward a recording medium according to their time inthe field.

Another object of this invention is to provide ink droplet printingapparatus in which the ink droplets used for printing are equallycharged and the deflection field is electrically or magneticallyenergized for regular intervals of time to establish different droplettrajectories.

Another object of this invention is to provide ink droplet printingapparatus in which the droplets are se lectively charged at either oftwo levels and may optionally be synchronously charged with dropletproduction or asynchronously charged.

A still further object of this invention is to provide ink dropletprinting apparatus in which droplets are given deflection trajectoriesaccording to the time that is spent in either an electrostaticdeflection field or a magnetic deflection field.

Another object of this invention is to provide ink droplet printingapparatus having a pair of selectively energizable deflection fieldsbetween a droplet source and recording medium in which droplets aregiven deflection in proportion to the time spent in either of saidfields.

SUMMARY OF THE INVENTION The foregoing objects are attained inaccordance with the invention by serially producing a stream oflike-charged ink droplets, directing them through a selectivelyenergizable deflection field toward a recording medium, and selectivelyenergizing the field in accordance with the position of the dropletstherein so as to cause said droplets to assume a trajectory dependentupon the time each droplet is subjected to the field. In a simple case,the field is merely turned on and then off when the series of dropletsis between the plates. Thereby, each successive droplet later in theseries is subjected to the field for a longer period and will have agreater deflection from its initial path of travel. The droplets arepreferably produced in sufficient number to record a full line of therecording matrix if every droplet is present. When using chargeddroplets in an electrostatic field, each of the droplets to be used inthe series is given a like charge and droplets to be discarded are givena different or no charge. Charging pulses may be provided for apredetermined time until the selected series is fully charged or may besynchronously applied by energizing the droplets as each is produced.The ink drop printing apparatus of the invention can also be used withmagnetic ink droplets. Of course, in this case no charge is placed onthe droplets but they are likewise produced in a sufficient number in aseries to complete one line of the matrix in the case where a full lineis required. Unwanted magnetic droplets may be deflected by an auxillarydevice from the character forming deflection field. The deflection fieldis preferably energized for regularly recurring time intervals and themagnitude of the energizing signal may be constant or in some casesvaried.

Because of the simplified deflection control means much of the expensenecessitated by the circuits for the electrostatic control meansheretofore known has been eliminated. Ink droplet charging can be donein a binary fashion either synchronously or asynchronously and thedeflection field energization may be accomplished on a regularlyrecurring time cycle even though relatively complex characters have tobe formed. The

invention has the advantage of not being restricted to fieldenergization signals of constant amplitude but other signals such asramp or step signals may be applied if desired to produce the necessarydeflection trajectories for the droplets. The deflection technique issuitable for use with either electrostatic deflection fields or withmagnetic deflection fields and carries with it the above namedadvantages in either case.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates anink drop deflection apparatus constructed in accordance with theprinciples of the invention.

FIG. 2 is a timing diagram showing relationship between a signal appliedto a deflection field and the impact positions of ink dropletsresponding thereto.

FIG. 3 is a modification of the apparatus shown in FIG. 1 in which asecond selectively energizable deflection field has been added to enabletwo dimensional deflection.

FIGS. 4a and 4b illustrate another waveform that may be applied to thedeflection field and the relationship of the droplet trajectories inaccordance therewith.

FIG. 5 is a diagram of'an ink droplet printing apparatus in which agutter is used to receive all unwanted ink droplets.

FIG. 6 illustrates an aperture plate in conjunction with the apparatusof FIG. 3 in which improperly charged droplets and unwanted droplets canbe eliminated.

FIG. 7 is a schematic diagram of ink droplet printing apparatus formagnetic ink which incorporates the principles of the invention.

FIG. 8 is a schematic diagram of magnetic ink dropletdeflection-apparatus in which unwanted droplets can be eliminated.

FIG. 9 is a timing diagram showing both a time and amplitude variableenergization signal for a magnetic deflection field and showing therelative trajectories of ink droplets deflected by the field soenergized.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. I astream of ink droplets 10 issues from a nozzle 11 which is supplied withink under pressure from source 12. The nozzle and ink source, which maybe of types well known in the art, produce a stream of ink in the orderof 0.001 inches in diameter which breaks up into individual droplets inthe vicinity of the charging electrode 13. As each droplet breaks fromthe filament of ink issuing from the nozzle, it carries with it anelectric charge. In the diagram shown, each droplet receives the samecharge and the droplets pass serially between a pair of deflectionelectrodes 14 and 15 which areeach connected to opposite polarities of atime sequence deflection signal generator 16. The generator periodicallyenergizes plates l4, 15 to create a transverse electrostatic field ofthe polarity indicated. At the moment, it may be assumed that generator16 produces square wave pulses which vary between zero and a positivevalue. The system is synchronized such that the deflection plates areinitially uncharged and the droplets are produced in series in a group.When the first droplet of the group reaches the end of deflection plates14 and 15, to the right, and is about to emerge therefrom, the lastdroplet ofthe group has-just entered between the plates. At this time,an electric field at a fixed value is established between plates 14 and15 from signal generator'l6 and will remain until the last droplet inthe series reaches the right hand edge of the plates.

When this occurs, each of the equally charged droplets in the group willbe influenced by the electric field between plates 14 and 15 for adifferent amount of time. The first droplet of the group which is aboutto emerge from the plates will experience electric field for theshortest amount of time and the last droplet of the group, which hasjust entered between the plates, will experience the field for thegreatest amount of time as it travels the entire length of thedeflection plates. Intermediate drops of the groups will be influencedby the electric field for differing time periods and will acquire atransverse velocity component proportional to the time-integral of thefield they experience. Since they have a substantially constantvelocity, this is, in turn, proportional to the distance integral of thefield, from the position of the droplet at the instant the field isturned on to the end of the field region or termina tion of the field.The first droplet will experience little or no deflection as it leavesthe field region at the time the field is set up, whereas the last dropis fully deflected since it travels the full length of the field regionunder the influence of the field. The uniformly spaced intermediatedrops acquire equal increments of transverse velocity because of theelectric field distribution along the length of the deflection plates 14and 15 is uniform. After traveling along the trajectories toward therecording surface, not shown, the deflection droplets are arranged toproduce a line scan which is approximately linear. The deflection platescan be of a length to allow sufficient droplets therebetween to comprisea character stroke or one line of a matrix arrangement of droplets.

If the incoming stream of droplets is continuous and uniformly spaced, anew group is located in position between deflection plates 14 and 15 atapproximately the time the last drop of the first group of droplets hasleft the deflection plate region. This second group of droplets is givena line scan deflection because the deflection field is now reduced tozero because of the termination of the square wave signal from generator16. The difference with the second group of droplets is that the lastdroplet in that group receives little or no deflection because theelectric field between the deflection plates is turned off atapproximately the time it enters the region between the plates. Theforemost drop of the group is fully deflected because electric field wason during nearly the whole of its transit time. Likewise, theintermediate droplets are deflected proportional amounts. Thus, the scandirection reverses for the second group of droplets.

If a third group of droplets follows normally spaced behind the secondgroup, it enters the region between deflection plates 14 and 15 when theelectric field is zero and is scanned when the field is switched onagain by the next positive square-wave pulse from generator 16. Theresult is a scan moving back and forth in a vertical direction.Naturally the scan can be made to travel back and forth in a horizontaldirection if the deflection plates are rotated degrees about the nominaldroplet path.

FIG. 2 illustrates the relationship between the deflection of the groupsof droplets discussed above and the square wave voltage signal appliedto deflection plates 14 and 15 of FIG. 1. It will be seen that thedroplets are proportionately deflected in one direction when the squarewave pulse is present to establish a transverse deflection field, andthe droplets are deflected in the opposite direction when the deflectionvoltage returns to zero.

In FIG. 1 a scheme is shown for deflecting the ink droplets back andforth in one dimension, that is, the vertical direction. Since all thedroplets have the same charge, it is possible, if required, to provideanother scan direction by passing the droplets between a second pair ofdeflection plates, positioned, for example, orthogonal to the first pairof deflection plates. With this technique, a matrix scan can be createdwithout moving the recording surface. Referring to FIG. 3, a systemhaving two pairs of deflection plates is shown. A stream of equallycharged ink droplets is produced using a structure described for FIG. 1.The stream of droplets is directed between the first pair of deflectionplates -21 which are connected to a source of square wave voltage 23similar to signal source 16 of FIG. 1. The droplets are deflected backand forth in a one dimensional scan as described in relation to FIG. 1,except that the direction of scan is horizontal due to the position ofdeflection plates 20 and 21. The deflected droplets emerging from plates20 and 21 pass between a second pair of deflection plates 24 and 25where they are deflected in the second direction such as vertical toproduce a second scan that is relatively slow. Because of the relativeslowness of the scan, the droplet transit time is not critical and thescan can be established by a field produced by a ramp voltage from adeflection signal generator 26 connected to plates 24 and 25, just aswith the conventional cathode ray tube deflection signal. Transit timeof the droplets through deflection plates 24 and 25 may have the effectof delaying the deflection and distorting it fora period equal to thetransit time near the leading and trailing edges of those plates. Theseeffects can be nullified by initiating the ramp voltage before the firstactive droplet of the complete raster scan enters the electric fieldregion between the second set of deflection plates 24 and 25 and endingonly after the last active droplet has emerged.

The deflection voltage from signal generator 26 need not be a rampvoltage; a staircase deflection voltage signal such as applied todeflection plates 20 and 21 may also be employed provided thatdeflection plates 24 and 25 are long enough to encompass all thedroplets in the raster. Whether a ramp deflection voltage signal or astaircase voltage signal is used, a zig-zag raster is obtained asillustrated on recording medium 27.

The invention has been described assuming that the signal generatorproduces regularly spaced square waves and that the charged ink dropletsare produced continuously. The result was a zig-zag raster scan on therecording medium. If the droplets are produced in groups of a lengthsufficient to produce one line of a matrix, with a gap created betweendroplet groups, it will be obvious that parallel lines having a singlesweep direction can be produced. With this in mind, another modificationof droplet control is shown in FIGS. 4a and 4b.

IN FIGS. 4a and 4b, there is shown a technique of extending the linelength in a matrix wherein the deflection electrodes are halfthe lengthofa series of droplets which are to make up the matrix line of print.This is accomplished by square wave signals which occur alternately,positively and negatively with respect to a zero potential line asindicated in FIG. 4a. The time in this example is divided into equalincrements with the beginning and ending of the increments designated:1, t2, t3, :4. In FIG. 4b, a pair of deflection plates 30 and 31 areshown, between which successive groups of serially arranged ink dropletsare directed toward a recording medium not shown. Considering the groupof droplets denoted by heavy lines, at time [1, a positive square waveis applied to deflection plates 30 and 31 for the time 11 and 12. Asseen in FIG. 4b, the first droplet of the series of charge droplets isabout to enter the deflection field and will be subjected to thetransverse force of the field during its entire traversal from thebcginning ofthe deflection plates to the end of the deflection plates.The succeeding three drops will experience the deflection force, eachfor a slightly less interval of time and the fifth drop in the serieswill just start to enter the deflection field at time 12 when the squarewave signal is terminated. Each of the first four droplets will havereceived varying transverse velocity components during the passagethrough the field and during the time required for the fifth droplet totravel to the end of the deflection field, which is not energized, notransverse forces will be experienced by the last five droplets.However, at time [3, a negative square wave is applied to the deflectionelectrodes and as the last four droplets continue in such a field, theywill receive transverse velocity components in the direction opposite tothe first four. It will be noted that the center droplet of the seriesdoes not experience any deflection force, since the deflection field wasterminated as it entered the plates 30, 31 and the field was energizedjust as that droplet left the deflection plates. With this technique, alonger matrix can be generated at the recording surface.

The description thus far has indicated that a series of dropletsgenerated should be formed in groups to coincide with the regularlyrecurring deflection field energization. FIG. 5 illustrates how inkdroplets can be formed continuously and then selectively eliminated toform groups or to form voids within a group which may be required forthe matrix line of a character being formed. Droplets issue continuouslyfrom nozzle 35 and pass between charging electrodes 36, then betweendeflection electrodes 38 and 39 while proceeding toward recording medium40. However, charging electrodes 36 are intermittently controlled toplace charges only on certain of the droplets issuing. The unchargeddroplets, as they pass through the deflection field, cannot be deflectedfrom their nominal path, and will be collected in a gutter 41 which, asis usual in the art, is connected by a vacuum pump to the ink supply forthe nozzle for reuse. Those droplets that are charged will be deflectedin accordance with the excitation voltage on deflection plates 38 and39. With the apparatus as shown, it is preferable to place a biasvoltage on deflection plates 38 and 39 to deflect all charged dropletsabove gutter 41. The applied control signal can then be superimposedupon the bias signal to achieve the desired droplet deflection.

It has been mentioned above that the charge voltage for droplets at thecharging electrode may be asynchronously applied rather thansynchronously. By this is meant that the charge voltage is not appliedin timed relation with each droplet at breakoff from the filamentextending from the nozzle. As seen in FIG. 6, droplets issue from nozzle35 and form droplets in the vicinity of charge electrodes 36 which arecontrolled by charge circuit 37. Charge circuit 37 will apply the binary(charge or no charge) signal for the time necessary to charge thedroplets required within or for a matrix line on the recording medium.As both the charged and uncharged droplets proceed toward the recordingmedium 40, they pass between two pairs of orthogonally disposeddeflection plates. One pair is selection electrodes 42 and 43 controlledby selection voltage circuit 44. This circuit is essentially acontinuous bias voltage which has the effect of deflecting all chargeddroplets from the uncharged droplets. Simultaneously all dropletsproceed between vertically disposed deflection electrodes 38 and 39which operate with the time dependent on-off deflection signal asdescribed earlier with regard to FIGS. 1-4. Interposed between recording medium 40 and the selection and deflection electrodes 42, 43 and 38,39- is a mask or plate 45 which has a gutter opening 46 and a printopening 47. Opening 46 communicates with'a duct 48 which returns to asump, not shown. Mask 45. is fitted with a collection channel 50 at thebottom thereof which is connected to a duct 51 which likewise returns tothe sump.

In the operation of the structure of FIG. 6, droplets issuing fromnozzle 35 are either charged or not charged depending upon whether theyare required for printing. Those desired are all charged to a commonlevel, while those not required are given no charge. As the continuousseries ofdroplets passes into the electric field established betweenelectrodes 42, 43, those carrying a charge will be deflected towardopening 47 in mask 45. Droplets uncharged will continue to opening 46 inthe mask and return through duct 48 to the sump for reuse. Sincecharging has occurred asynchronously some droplets. may have receivedtheir charge during the time of transition from the zero voltage onplates 36 to full value or during the transition in the oppositedirection and not be fully charged or uncharged. These droplets whenpassing between electrodes 42 and 43 will be only partially deflectedtoward opening 47 from opening 46 and will impact mask 45 between thetwo openings thereby draining into channel 50. When the fully chargeddroplets reach vertical deflection electrodes 38 and 39, the desiredtime deflection signal is applied or removed from those electrodes toproduce the required vertical change in trajectory. These droplets willcontinue through opening 47 and impact recording medium 40. Deflectionelectrodes 38 and 39 are controlled as described with regard to FIG. 1.

The technique of time dependent deflection of ink droplets is alsoreadily adaptable to printing with magnetic ink, as illustrated in FIG.7. Magnetic ink is supplied from pressurized source 60 to nozzle 61 andissues therefrom as a stream, subsequently breaking into droplets. Thedroplets, however, are not charged as is the case with electrostaticdeflection. The droplets are directed between the pole pieces 62 of anelectromagnet 63 which is energized by winding 64 for selective periodsof time to subject each of the droplets in the series to differentdurations of transverse forces as the droplets traverse the nominalflight path. Energization is done with an intermittently controlledsignal generator 65. During their travel, the droplets enter themagnetic field of the electromagent 62 and experience a transverse forcein the direction of the higher density flux paths. In other words, thetransverse forces will be downward and deflection will occur inproportion to the time each droplet is subjected to the applied forces.As described with reference to FIG. 1, if successive series of dropletsare formed and directed through the magnetic field, a signal such as aregularly applied square wave can be used to produce successive parallellines on recording medium 66 if the recording medium is moved laterallyof the stream.

Since it is more practical to generate magnetic ink dropletscontinuously, unwanted droplets must be eliminated. One technique forselective elimination is shown in'FlG. 8. Droplets of magnetic ink areformed by nozzle 61 and directed as in FIG. 7 between pole pieces 62 ofelectromagnet 63 having winding 64. The winding is controlled by timesequence deflection signal generator 65. The ink droplets have a nominalpath which will impact recording medium 66 at the desired print area. Tothis point the structure of FIG. 8 is similar to that of FIG. 7;however, in order to achieve the selectivity of ink droplets, horizontalselector magnet 67 is arranged so that its pole pieces 68 are onopposite sides above and below the droplet path. The selector magnetalso has a control winding 69 thereon which is connected with a suitablesignal source for intermittently applying energizing current to producea magnetic flux field about the droplet path. The selector magnet 67 isa thin ferromagnetic material which is less than the drop-to-dropspacing so that when energized the selector magnet will operate only ona single drop. As droplets pass along their nominal path the selectormagnet can be intermittently energized which will create a leftwarddeflection due to the flux gradient causing the selected drops to departsufficiently from the desired drops to enter a gutter 70. Desired dropswill continue to pass between the pole pieces 62 of the verticaldeflection magnet 63 so that ink droplets are deflected according to thetime subjected to the field of magnet 63. Droplets deflected from thenominal path by selector magnet 67 will also be vertically influenced bythe electromagnet 63 but gutter 70 is made to have a sufficiently longvertical opening to catch such deflected droplets.

In certain instances, particularly deflection of magnetic ink, theamount of droplet deviation provided by an electromagnet may not besufficient to produce the length ofline scan desired. This may be due tothe electromagnet characteristics or the lack of space between thenozzle and recording medium. A technique of extending the scan distanceis to superimpose a ramp signal on the time sequence deflection signalwhich is applied to the vertical scan magnet. This, of course, applies agreater transverse force to the droplets during the time that they arewithin the activating magnetic field. The deflection signal may belonger than the traversal time required for a droplet through themagnetic field. It should also be noted that such a technique is equallyapplicable to electrostatic embodiment of FIG. 1. Although a ramp hasbeen shown in FIG. 9, other wave forms may be employed to attain thedesired droplet deflection.

There has been described improved ink jet printer structure which usesink droplets having a binary type of charge, being either charged oruncharged and which permits the use of a simplified deflection circuit.The technique is also adaptable to magnetic ink jet printers.

While the invention has been particularly shown and described withreference to preferred embodiments, it will be understood by thoseskilled in the art that the foregoing and other changes in form anddetails may be made therein without departing from the spirit and scopeof the invention. What is claimed is: 1. A fluid drop control systemcomprising: means for directing a series ofdrops ofmarking fluid of likedeflection characteristics along a path;

selectively energizable means adjacent said path for establishing adeflection field simultaneously encompassing said drop series and havinga force component transversely of said path acting to deflect said dropsmoving along said path; and

means for energizing said deflection means for a predetermined time tosubject each drop in said series of drops to said transverse force fordifferent times for unidirectional deflection and impart to each drop insaid series a different trajectory from said path beyond said deflectionmeans according to the time subjected to said force.

2. Apparatus as described in claim 1 wherein said energizing means isoperable for regular intervals of time.

3. Apparatus as described in claim 1 wherein said deflection means isenergizable by electrical signals.

4. Apparatus as described in claim 1 wherein saiddirecting meansproduces drops in a series uniformly spaced from each other.

5. Apparatus as described in claim 1 wherein the energy supplied by saidenergizing means is of a constant level during said predetermined time.

6. Apparatus as described in claim 1 wherein said means for energizingsaid deflection means is also operable to vary the magnitude ofenergization during each predetermined time period.

7. A fluid droplet marking system comprising:

a recording medium:

means for directing droplets of marking fluid of like deflectioncharacteristics of substantially uniform size serially along a pathtowards said recording medium;

selectively energizable deflection means between said directing meansand said recording medium for establishing a force componentencompassing a series of said droplets and acting transversely thereonas said droplets are moving along said path to deflect said dropletstherefrom; and

means for uniformly energizing said deflection means for a predeterminedtime to simultaneously act on a plurality of said droplets to induceunidirectional deflection and to cause each said droplet in said seriesto be deflected according to the time subjected to said force and followa different trajectory from said path toward said recording medium.

8. Apparatus as described in claim 7 comprising second selectivelyenergizable deflection means between said directing means and saidrecording medium for establishing a force component transversely of saidpath and in a direction different from the force component of thefirst-mentioned deflection means to deflect said drops from said path;and

second means for energizing said second deflection means for a secondpredetermined time for altering the trajectory of selected ones of saiddroplets passing from the first deflection means toward said recordingmedium.

9. Apparatus as described in claim 8 wherein said deflection means andsaid second deflection means are arranged to act simultaneously on saiddroplets when energized.

10. Apparatus as described in claim 7 further including means forinhibiting certain selected droplets from said directing means fromreaching said recording medium.

11. Apparatus as described in claim 7 wherein said deflection means is apair of electrically energizable plates on opposite sides of said pathand said energizing means produces an electrical field therebetween; and

further including charging means between said directing means and saiddeflection means for establishing a uniform electrical charge onselected ones of said droplets.

12. Apparatus as described in claim 11 wherein said charging meansincludes a source of binary voltage signal selectively operable forapplying charging voltage only to selected ones of said droplets fromsaid directing means, leaving others of said droplets in said seriesuncharged and not deflectable by said deflection means; and

interceptor means located between said directing means and saidrecording medium for intercepting and collecting said unchargeddroplets. 13. Apparatus as described in claim 7 wherein said energizingmeans applies a square wave signal to said deflection means.

14. Apparatus as described in claim 7 wherein said energizing meansincludes means to establish a bias energy level on said deflectionmeans.

15. A fluid drop control system comprising: means for producing drops ofmarking fluid having like deflection characteristics in a force fieldand directing a series of said drops along a path;

selectively energizable means adjacent said path for establishing adeflection fleld simultaneously encompassing said drop series and havinga force component transversely of said path acting to deflect saidseries of drops moving along said path; and

means for energizing said deflection means for a predetermined time tosubject each drop in said series of drops to said transverse force fordifferent times according to the position of each said drop in saidseries while moving past said selectively energizable means and impartto said drops unidirectional deflection and in different trajectoriesfrom said path beyond said deflection means.

1. A fluid drop control system comprising: means for directing a seriesof drops of marking fluid of like deflection characteristics along apath; selectively energizable means adjacent said path for establishinga deflection field simultaneously encompassing said drop series andhaving a force component transversely of said path acting to deflectsaid drops moving along said path; and means for energizing saiddeflection means for a predetermined time to subject each drop in saidseries of drops to said transverse force for different times forunidirectional deflection and impart to each drop in said series adifferent trajectory from said path beyond said deflection meansaccording to the time subjected to said force.
 2. Apparatus as describedin claim 1 wherein said energizing means is operable for regularintervals of time.
 3. Apparatus as described in claim 1 wherein saiddeflection means is energizable by electrical signals.
 4. Apparatus asdescribed in claim 1 wherein said directing means produces drops in aseries uniformly spaced from each other.
 5. Apparatus as described inclaim 1 wherein the energy supplied by said energizing means is of aconstant level during said predetermined time.
 6. Apparatus as describedin claim 1 wherein said means for energizing said deflection means isalso operable to vary the magnitude of energization during eachpredetermined time period.
 7. A fluid droplet marking system comprising:a recording medium: means for directing droplets of marking fluid oflike deflection characteristics of substantially uniform size seriallyalong a path towards said recording medium; selectively energizabledeflection means between said directing means and said recording mediumfor establishing a force component encompassing a series of saiddroplets and acting Transversely thereon as said droplets are movingalong said path to deflect said droplets therefrom; and means foruniformly energizing said deflection means for a predetermined time tosimultaneously act on a plurality of said droplets to induceunidirectional deflection and to cause each said droplet in said seriesto be deflected according to the time subjected to said force and followa different trajectory from said path toward said recording medium. 8.Apparatus as described in claim 7 comprising second selectivelyenergizable deflection means between said directing means and saidrecording medium for establishing a force component transversely of saidpath and in a direction different from the force component of thefirst-mentioned deflection means to deflect said drops from said path;and second means for energizing said second deflection means for asecond predetermined time for altering the trajectory of selected onesof said droplets passing from the first deflection means toward saidrecording medium.
 9. Apparatus as described in claim 8 wherein saiddeflection means and said second deflection means are arranged to actsimultaneously on said droplets when energized.
 10. Apparatus asdescribed in claim 7 further including means for inhibiting certainselected droplets from said directing means from reaching said recordingmedium.
 11. Apparatus as described in claim 7 wherein said deflectionmeans is a pair of electrically energizable plates on opposite sides ofsaid path and said energizing means produces an electrical fieldtherebetween; and further including charging means between saiddirecting means and said deflection means for establishing a uniformelectrical charge on selected ones of said droplets.
 12. Apparatus asdescribed in claim 11 wherein said charging means includes a source ofbinary voltage signal selectively operable for applying charging voltageonly to selected ones of said droplets from said directing means,leaving others of said droplets in said series uncharged and notdeflectable by said deflection means; and interceptor means locatedbetween said directing means and said recording medium for interceptingand collecting said uncharged droplets.
 13. Apparatus as described inclaim 7 wherein said energizing means applies a square wave signal tosaid deflection means.
 14. Apparatus as described in claim 7 whereinsaid energizing means includes means to establish a bias energy level onsaid deflection means.
 15. A fluid drop control system comprising: meansfor producing drops of marking fluid having like deflectioncharacteristics in a force field and directing a series of said dropsalong a path; selectively energizable means adjacent said path forestablishing a deflection field simultaneously encompassing said dropseries and having a force component transversely of said path acting todeflect said series of drops moving along said path; and means forenergizing said deflection means for a predetermined time to subjecteach drop in said series of drops to said transverse force for differenttimes according to the position of each said drop in said series whilemoving past said selectively energizable means and impart to said dropsunidirectional deflection and in different trajectories from said pathbeyond said deflection means.